Drill string fitting

ABSTRACT

A fitting for reducing friction between a drilling string and the wall of a well. In a first aspect the fitting has recesses ( 6 ) provided along the bore of the fitting to lubricate the interface between the fitting and the drill string to minimise friction. In a second aspect a fitting is provided on a drill string having rotatable roller means ( 21 ) which can rotate about a point of rotation ( 23 ) so as to minimise both axial and rotational friction. According to a third aspect the fitting comprises an inner section ( 30 ) secured to a drill pipe ( 35 ) or other fitting and an outer section ( 31 ) rotatable about the inner section ( 30 ). Preferably a sealed bearing ( 36, 42-47, 37, 38 ) is provided between the inner section ( 30 ) and outer section ( 31 ).

TECHNICAL FIELD

The present invention relates to a fitting for reducing friction betweena drill string and the wall of a well. More particularly, but notexclusively, in a first aspect the present invention relates to afitting having a plurality of longitudinal recesses enabling lubricationbetween the fitting and a drill string using drilling fluid. Accordingto a second aspect there is provided a fitting having rotatable rollersto reduce both axial and rotational friction. According to a thirdaspect there is provided a fitting having an outer section rotatablerelative to an inner section secured about a drill string.

BACKGROUND OF THE INVENTION

The depth to which and angle at which a well can be drilled are oftenlimited by the degree of friction experienced by the drill string. Thelife of a drill string may also be reduced due to friction. Withincreasing environmental concerns it is also becoming less acceptable toreduce friction by injecting chemicals down a well. Using wellstreamfluids as a lubricant results in drill string wear due to particulatematter carried in the fluids. Further, currently available similarfittings cannot be rebuilt or reconditioned.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a fitting whichreduces the friction on a drill string or at least to provide the publicwith a useful choice.

According to a first aspect of the invention there is provided a fittingfor reducing friction between a fitting and a section of a drill stringor further fitting on a drill string, said fitting comprising a bodyhaving a tubular bore provided with a plurality of longitudinallyextending recesses spaced circumferentially about the bore, dimensionedto lubricate the interface between the fitting and the drill string orfurther fitting with fluid in a drilling well, wherein rollers areprovided about the periphery of the body to reduce friction in the axialdirection.

Preferably the bore of the fitting has a polygonal cross-section. Inanother embodiment the fittings may have a substantially circularcross-section and the sleeve may have a polygonal cross-section. Thefitting may preferably be formed as a two part casing which can besecured to an assembled drill string.

According to a further aspect of the invention there is provided afitting for engagement to a drill string or further fitting having abody with a bore therethrough provided with a plurality of roller meanson the exterior of the body, each said roller means having one or moreroller provided thereon and being rotatable relative to the body aboutan axis transverse to the axis of the bore, the arrangement being suchthat the roller means can rotate relative to said body to facilitatereduction of rotational and axial friction.

Preferably, the rollers have a substantially tapered cylindrical formand rotate about an axis transverse to the axis of rotation of theroller means. The body may be of two part construction and the rollersare preferably formed of a nylon or ceramic material.

According to a further aspect of the invention there is provided afitting for engagement with a drill string or further fitting comprisingan inner section for securement to a drill string or further fitting, anouter section for securement about said inner section, a bearing locatedbetween the inner section and outer section, seals provided at eitherend of the fitting between the inner section and outer section andpressure compensating means for maintaining the pressure within thebearing substantially the same as the external pressure.

Preferably a plurality of fins project radially from the outer sectionwhich are profiled to reduce drag in the axial direction.

BRIEF DESCRIPTION OF THE DRAWINGS

Further aspects of the invention will become apparent from the followingdescription which is given by way of example of possible embodimentswith reference to the accompanying drawings in which:

FIG. 1: Shows a two part fitting having a polygonal bore.

FIG. 2: Shows the interface between a drill string and the interiorpolygonal bore of the fitting shown in FIG. 1.

FIG. 3: Shows a section of drill string having collars at either end forreceiving the fitting of FIG. 1 therebetween.

FIG. 4: Shows an end view of the fitting of FIG. 1.

FIG. 5: Shows an end view of the fitting of FIG. 1 engaged with thesleeve shown in FIG. 3.

FIG. 6: Shows a front view of the fitting of FIG. 1 showing a partialcross-sectional view.

FIG. 7: Shows a fitting having rotatable rollers provided on the bodythereof.

FIG. 8: Shows a cross-sectional view of a rotatable roller shown in FIG.7.

FIG. 9: Shows a cross-sectional view of a roller of a rotatable rollershown in FIG. 7 or FIG. 8.

FIG. 10: Shows a perspective view of a fitting according to a thirdembodiment.

FIG. 11: Shows a cross-sectional view along the axis of the fittingshown in FIG. 10.

FIG. 12: Shows an enlarged view of the seal arrangement shown in FIG.11.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring firstly to FIGS. 1 to 6, there is shown a fitting for reducingfriction on a pipe string. The fitting comprises a body formed of twoparts 1 and 2 which may be secured together by bolts which pass throughapertures 3. A plurality of rollers 4 are provided about the outside ofthe fitting to reduce longitudinal friction on the pipe string. The bore5 of the body sections is polygonal so as to provide a number oflongitudinal recesses 6 between the body 1 and a sleeve 7.

Drilling pipe is usually forged from high tensile steel. The outsidesurface is typically rough. The preferred method of securing the fittingof the invention to a drilling pipe is as follows. Firstly, a section ofthe drilling pipe is machined so as to have a relatively smooth outsidesurface. The two halves 7 a and 7 b of the sleeve shown in FIG. 3 arethen secured to the drilling pipe by bolts etc passing through theapertures of collars 8 a, 8 b, 9 a and 9 b. Once the sleeve has beensecured to a section of pipe, the two halves 1 and 2 of the fitting aresecured about sleeve portions 7 a and 7 b and secured by bolts passingthrough apertures 3.

Collars 8 and 9 restrict the longitudinal movement of the fitting. Thefitting is however free to rotate about sleeve 7. Accordingly, frictiondue to rotation of the drilling rig is minimised due to the fluidlubricant provided in recesses 6 between body sections 1 and 2 andsleeve 7. Axial friction is reduced by rollers 4 which minimise frictionbetween the wall of the well and the fitting in the longitudinaldirection.

It would be possible to secure the fitting directly about a section ofpipe. This would however not reduce friction to the same extent as byproviding smooth sleeve 7. Where a new section of pipe is beingmanufactured, it may of course be provided with a smooth section havingseparate collars 8 and 9 integrally formed at either end thereof forreceiving the fitting.

Although the interior bore 5 of the fitting has been described aspolygonal, it will be appreciated that other shapes of internal bore(eg: sinusoidal) may be provided as long as suitable recesses areprovided between the sleeves and the body of the fitting to minimisefriction. In some applications the bore 5 of the fitting may bespiralled to minimise the effect of transitions from one recess toanother and to promote fluid flow through the fitting. Filtering means,such as wire mesh may preferably be provided at either end of thefitting to prevent large debris entering the recesses.

In viewing FIG. 5 it will be seen that each roller 4 is secured to body1 by a pin 10 passing through roller 4. Pin 10 may pass through aperture12 in body 1 into recess 11. The aperture 12 may then be welded closedto prevent the pin 10 be removed.

Roller 4 may preferably be formed of a ceramic or nylon material.Ceramic materials have the advantage that they exhibit excellent wearproperties and have a low friction coefficient. Newly developed ceramicshave acceptable “ductility” properties and are easily formed. Ceramicsare also very stable at high temperatures and are self lubricating, sodo not require oil-based lubrication. Ceramics materials are notsusceptible to Theological failure or welding either. One of the keyadvantages, however, is that the density of ceramic materials is suchthat if a roller breaks the pieces can be circulated out of the wellbore, unlike steel fragments which sink to the bottom of the well andinterfere with drilling.

As shown in FIG. 6 a protective section 13 may be provided between thecollars 8 a, 8 b and 9 a, 9 b and between the rollers 4 to create asmooth exterior profile so that parts of the fitting do not catch as thefitting is moved up and down in a well.

It is estimated that using fittings as herein before described aboutdrill pipe joints will reduce the drag by at least 30%. This enableswells to be drilled to greater displacements and at higher angles.Further, expensive drill pipe is protected and the fitting is exposed tomost of the wear. The fitting is designed for easy retrofitting toexisting pipe and so avoids the need for large expenditure on new pipestrings.

FIGS. 7 to 9 show a second embodiment of the invention. The aim again isto reduce longitudinal and rotational friction on a pipe string orfittings employed therewith. A simple one part construction is describedalthough it will be appreciated that a two part body as previouslydescribed, may be employed.

Body 20 is provided with a plurality of rotatable roller means 21, shownin more detail in FIG. 8. Rotatable roller means 21 are substantiallydisc-shaped and have a cylindrical recess 22 located at the centrethereof. Pin 23 of body 20 engages in recess 22 so that the rotatableroller means 21 is rotatable about pin 23. Circumferential flange 24 issecured after roller means 21 has been inserted and retains the rollermeans 21 in place in use. Circumferential flange 24 may be securedfirmly in place by welding etc. The rotatable rollers 25 are securedoff-centre from pin 23 so that the rotatable roller means 21 may berotated as it is exposed to different types of frictional force (i.e.longitudinal or rotational).

From the above it will be apparent that when body 20 experiences purerotation relative to the wall of a well, rollers 25 will not be able torotate (in the position shown in FIG. 7) and will cause the rotatableroller means 21 to rotate 90° so that the axes of the rollers arealigned with the axis of the drilling rig. When in this position, therollers can freely rotate to minimise friction. When the drill string ismoved purely in the longitudinal direction, the rollers will stay in theposition as shown in FIG. 7 so that they may freely rotate to reducelongitudinal friction. It will be appreciated that when there is acombination of rotational and axial movement the axis of the rollerswill be somewhere between the two positions described above.

Referring to FIGS. 10 to 12 a third embodiment will be described. Thefitting of the third embodiment comprises an inner section 30 and anouter section 31 which is rotatable about inner section 30. Innersection 30 is adapted to be secured about a drill pipe which passesthrough bore 32. Inner section 30 may be of two part construction(similar to that shown in FIG. 3) where the two parts are securedtogether by bolts or similar fastening means. Outer section 31 maysimilarly be of two part construction and be secured about inner section30. Outer section 31 is provided with a plurality of fins 33 extendingradially from body 34.

FIG. 11 shows a cross-sectional view along the axis of the fitting shownin FIG. 10. In this case the fitting is secured to a drill pipe 35. Alayer of friction reducing material 36 is provided between faces 42 to47 to reduce friction as outer section 31 rotates about inner section30. Layer 36 will preferably be formed of a plastics material such asnylon (zytel 70633L for example).

Seals 37 and 38 are provided at either end of the bearing formed by theinter-engaging faces 42 to 47 of inner section 30 and outer section 31and friction reducing layer 36. These seals serve to prevent the ingressof fluid from a well into the bearing. This greatly reduces friction onbearing surfaces, thus reducing wear and decreasing the torque requiredto drive a drill string.

Due to the sealed nature of the bearing a pressure compensating system39 is provided to compensate the pressure within the bearing as theexternal pressure varies. The pressure compensating system comprises adiaphragm 40 containing grease within region 41 which moves in and outof the bearing as external pressure varies. This prevents external fluidbeing drawn into the bearing as the external pressure increases.

The bearing journals 42 and 43 are preferably precision ground. Bearingsleeves may be provided if required. Sections 44 and 45, and 46 and 47of the bearing minimise friction when the outer section 31 is forced inthe axial direction relative to the inner section 30.

Referring now to FIG. 12, seal 37 is shown in detail. The seal is seento include a resilient seal 48 located within a recess 49 in outersection 31. Seal 48 is preferably formed of a fibre reinforced PTFE.

The profile of the fins 33 is shown to be semi-circular in FIGS. 10 and11. It is to be appreciated that other profiles may be employed whichreduce drag in the axial direction. The curved profile shown ispreferred due to its drag reduction in both directions. It is to beappreciated that rollers could be provided upon fins 31 to assist in thereduction of axial drag. The fins are preferably coated with a ceramiccoating such as CERAM-KOTE™.

Bearing surfaces 42 to 47 are preferably coated with a hard materialsuch as Technogenia “technopoudre” or similar. Channels are preferablyprovided in bearing surfaces 42 and 43 to facilitate the flow oflubricant. These channels will preferably be semicircular in profile andwill preferably spiral along the length of the journals (similar to therecesses 6 shown in FIG. 2).

This fitting may be mounted directly onto a drill pipe during productionor may be retrofitted to an existing drill pipe. Alternatively, thefitting may be provided on its own separate “sub” or mandrill, in whichcase the “sub” or mandrill may be screwed into the drill string betweentwo lengths of drill pipe.

It will thus be seen that the invention provides a number of simpleinexpensive fittings for reducing the friction experienced between adrill string and the wall of a well. The fittings may be used to protectthe joints of pipe strings or fitting tools as required. The inventionreduces friction and thus the required torque to drill a well. Reductionof friction also reduces drill string vibration and thus fatigue in thedrill string. The invention also minimises environmental damage by usinga water-based mud lubricant.

Where in the foregoing description reference has been made to integersor components having known equivalents then such equivalents are hereinincorporated as if individually set forth.

Although this invention has been described by way of example and withreference to possible embodiments thereof, it is to be appreciated thatimprovements and/or modifications may be made thereto without departingfrom the scope of the invention as defined in the claims.

Industrial applicability

The present invention may find particular application in the reductionof friction experienced by drilling strings.

What is claimed is:
 1. A fitting apparatus securable to a section of adrill string or a second fitting on said drill string, said fittingapparatus comprising: a body having a tubular bore, said tubular boreprovided with a plurality of longitudinally extending recesses spacedcircumferentially about the bore, said recesses dimensioned to receive alubricating fluid for substantially reducing rotational friction betweensaid fitting apparatus and said drill string, or between said fittingapparatus and said second fitting on said drill string; and rollersprovided about the periphery of the body to reduce friction in the axialdirection.
 2. A fitting apparatus as claimed in claim 1 wherein the boreof the fitting apparatus is polygonal in cross-section.
 3. A fittingapparatus as claimed in claim 1 wherein the recesses spiral along thelength of the bore.
 4. A fitting apparatus as claimed in claim 1 whereinsaid rollers are provided in banks about the circumference of the body.5. A fitting apparatus as claimed in claim 4 wherein each said bank ofrollers includes a protective mounting assembly which exposes only aportion of each said roller.
 6. A fitting apparatus as claimed in claim1 wherein the fitting apparatus is of two part construction adapted tobe secured about said drill string.
 7. A fitting apparatus as claimed inclaim 1 wherein a filtering means is provided at either end of thefitting apparatus to prevent debris entering the longitudinal recesses.8. A fitting apparatus as claimed in claim 1 said fitting apparatusbeing adapted to engage said second fitting, wherein said second fittingis a sleeve having collars at either end adapted to be secured to asection of said drill string with the fitting apparatus securedthereabout between said collars.
 9. A fitting apparatus as claimed inclaim 1 having a bore of substantially circular cross-section incombination with said second fitting for securement to a section ofdrill pipe wherein said second fitting has a substantially polygonalcross-section.
 10. A fitting apparatus for engagement to a drill stringor a second fitting on said drill string, said fitting apparatuscomprising: a body with a bore therethrough, wherein said bore ispolygonal in cross-section, and a plurality of roller means on theexterior of the body, each said roller means having one or more rollersprovided thereon and being rotatable relative to the body about an axistransverse to the axis of the bore, the arrangement being such that theroller means can rotate relative to said body to facilitate reduction ofrotational axle friction.
 11. A fitting apparatus as claimed in claim 10wherein the rollers includes rollers positioned away from the transverseaxis so as to rotate said roller means to keep the axis of said rollerssubstantially transversed to the direction of movement.
 12. A fittingapparatus as claimed in claim 11 wherein a plurality of rollers areprovided on each said roller means.
 13. A fitting apparatus as claimedin claim 10 wherein the roller means comprises a substantiallydisc-shaped member located within a corresponding recess in the body.14. A fitting apparatus as claimed in claim 13 wherein said disc-shapedmember includes a central bore which locates with a pin extendingoutwardly from said body.
 15. A fitting apparatus as claimed in claim 13wherein a plate is secured above the peripheral edge of each rollermeans to retain it within its recess.
 16. A fitting apparatus as claimedin claim 10 wherein the rollers are formed of a nylon or ceramicmaterial.
 17. A fitting apparatus as claimed in claim 10 wherein therollers have a substantially tapered cylindrical form and rotate aboutan axis transverse to the axis of rotation of the roller means.
 18. Afitting apparatus as claimed in claim 10 wherein the body is of two partconstruction so that it may be secured about a section of said drillstring.
 19. A fitting apparatus for engagement with a drill string orsecond fitting on the drill string, said fitting apparatus comprising:an inner section for securement to the drill string or second fitting,an outer section for securement about said inner section and rotatablerelative thereto, a bearing comprising a layer of friction reducingmaterial and located between said inner section and said outer section,seals provided at either end of said fitting apparatus between saidinner section and said outer section and pressure compensating means formaintaining the pressure within the bearing substantially the same asexternal pressure.
 20. A fitting apparatus as claimed in claim 19wherein the layer of friction reducing material is formed of a plasticsmaterial.
 21. A fitting apparatus as claimed in claim 20 wherein theplastics material is nylon.
 22. A fitting as claimed in claim 19 whereinthe bearing comprises first journal surfaces on said inner and outersections in the axial direction of said fitting apparatus and second andthird journal surfaces on said inner and outer sections extendingradially outwards to restrict movement of said outer section relative tosaid inner section in the axial direction.
 23. A fitting apparatus asclaimed in claim 19 wherein a plurality of fins project radially fromsaid outer section which are profiled to reduce drag in the axialdirection.
 24. A fitting apparatus as claimed in claim 23 wherein thefins have a curved profile.
 25. A fitting apparatus as claimed in claim19 wherein rollers are provided on the periphery of said outer sectionto reduce friction in the axial direction.
 26. A fitting apparatussecurable to a section of a drill string or a second fitting on saiddrill string, said fitting apparatus comprising: a body having a tubularbore, said tubular bore provided with a plurality of longitudinallyextending recesses spaced circumferentially about the bore, saidrecesses dimensioned to receive a lubricating fluid for substantiallyreducing rotational friction between said fitting apparatus and saiddrill string, or between said fitting apparatus and the second fittingon said drill string, wherein said tubular bore is polygonal incross-section; and, rollers provided about the periphery of the body toreduce friction in the axial direction.
 27. A fitting apparatus asclaimed in claim 26, wherein the recesses spiral along the length of thebore.
 28. A fitting apparatus as claimed in claim 26, wherein saidrollers are provided in banks about the circumference of the body.
 29. Afitting apparatus as claimed in claim 28, wherein each said bank ofrollers includes a protective mounting assembly which exposes only aportion of each of said rollers.
 30. A fitting apparatus as claimed inclaim 26, wherein said fitting apparatus is of two part construction,said fitting apparatus being adapted to be secured about said drillstring.
 31. A fitting apparatus as claimed in claim 26, furthercomprising: a first filter and a second filter, said filters beinglocated at a first and second end of said fitting apparatusrespectively, to prevent debris from entering said longitudinalrecesses.
 32. A fitting apparatus as claimed in claim 26, wherein saidfitting apparatus is configured to be engageable with a second fittingthat is a sleeve having collars at either end secured to a section ofthe drill string, said fitting apparatus being securable between thecollars.
 33. A fitting apparatus as claimed in claim 26, said fittingapparatus having a tubular bore of substantially circular cross-sectionin combination with said second fitting for securement to a section ofdrill pipe wherein said second fitting is substantially polygonal incross-section.
 34. A fitting apparatus for engagement with a drillstring or second fitting on said drill string, said fitting apparatuscomprising: an inner section for securement to said drill string or saidsecond fitting, an outer section for securement about said inner sectionand rotatable relative thereto, a bearing located between said innersection and said outer section, wherein said bearing comprises a layerof friction reducing material; seals provided at either end of saidfitting apparatus between said inner section and said outer section;and, a pressure compensator located between said bearing and theexterior of said fitting apparatus, said pressure compensator adapted tomaintain the pressure within said bearing substantially the same asexternal pressure.
 35. A fitting apparatus as claimed in claim 34,wherein the layer of friction reducing material is formed of a plasticsmaterial.
 36. A fitting apparatus as claimed in claim 35, wherein theplastics material is nylon.
 37. A fitting apparatus as claimed in claim34, wherein the bearing is filled with a lubricating fluid.
 38. Afitting as claimed in claim 34, wherein the bearing comprises firstjournal surfaces on said inner and outer sections in the axial directionof said fitting apparatus and second and third journal surfaces on saidinner and outer sections extending radially outwards to restrictmovement of said outer section relative to said inner section in theaxial direction.
 39. A fitting apparatus as claimed in claim 34, whereina plurality of fins project radially from said outer section which areprofiled to reduce drag in the axial direction.
 40. A fitting apparatusas claimed in claim 39, wherein the fins have a curved profile.
 41. Afitting apparatus as claimed in claim 34, said fitting apparatus furthercomprising rollers on the periphery of said outer section to reducefriction in the axial direction.